This invention relates to a method for manufacturing integrated circuit elements, liquid crystal display elements or the like by photolithography, which reduces detrimental influence due to properties of a substrate or acidity of a substrate surface on resist form, and to a substrate-treating agent composition for use in this method.
In the field of manufacturing integrated circuit elements, patterning technology to form finer patterns by lithographic process has made a progress and, in recent years, development of patterning technology enabling quarter micron-ordered fine patterning has been studied. In such lithographic process, a photoresist is applied to a substrate, a latent image of a mask pattern is created in the photoresist by exposure, then the latent image is developed using a proper developer solution to obtain a desired patterned resist. However, many substrates to be used have such a high reflectivity that, upon exposure, exposing light passing through the photoresist layer is reflected on the surface of the substrate and is again incident into the photoresist layer, which causes problem that desired patterns are not obtained or that patterns with some defects are formed due to the exposure, by the reflected light, of photoresist areas which is not to be exposed or due to interference between the exposure light and the light reflected by the substrate surface. This problem is not limited to the field of manufacturing integrated circuit elements but is common in the field of conducting super-fine processing by lithographic process, such as manufacture of liquid crystal display elements.
Various techniques have been investigated to solve the problems caused by the reflection. For example, there have been attempted a technique of dispersing in the photoresist a dye having absorption at the exposure wavelength, a technique of forming a bottom anti-reflective coating (BARC) or a top surface anti-reflective coating, a technique of top surface imaging (TSI), and a technique of a multi-layer resist (MLR). Of these, the technique of forming a bottom anti-reflective coating is at present most popularly employed. As the bottom anti-reflective coating, inorganic coatings and organic coatings are known. As methods for forming the inorganic coating, there are known, for example, methods of depositing an inorganic or metallic material by CVD (Chemical Vapor Deposition), vacuum deposition, sputtering or the like. In addition, as methods for forming the organic coating, there are known, for example, a method of applying a solution or dispersion of a dye in an organic polymer solution to a substrate, and a method of applying to a substrate a solution or dispersion of a polymer dye which has a chromophore bonded chemically to a polymer. Materials of these bottom anti-reflective coating and methods for forming the coating are described in, for example, Japanese Unexamined Patent Publication (JP-A) Nos. H6-75378 and H6-118656, WO9412912, U.S. Pat. Nos. 4,910,122 and 5,057,399, etc.
The bottom anti-reflective coating serves to absorb or weaken the light having passed through the resist layer depending upon thickness and absorption properties of the bottom anti-reflective coating, thus reflection of the light having passed through the resist layer from the substrate being prevented. On the other hand, however, some materials forming the bottom anti-reflective coating leave alkaline or acidic residues or provide alkaline or acidic substituents in or on the surface of the bottom anti-reflective coating. When acidic or alkaline substances exist in or on the surface of the bottom anti-reflective coating, there arises the problem that, if a chemically amplified resist is used as photoresist, an acid generated in the resist upon exposure is neutralized and deactivated with the alkaline residues or alkaline groups in or on the surface of the bottom anti-reflective coating or that basic components in the resist react with the acidic residues or acidic groups in the bottom anti-reflective coating, resulting in deterioration of cross-sectional profile of resist patterns formed.
For example, when the bottom anti-reflective coating is formed as a nitride coating according to CVD method, sometimes surface of the nitride coating is not plain and coating composition inside the coating is not uniform. In addition, under some conditions, part of the amino groups can remain and, when remaining, the residual amino groups are non-uniformly distributed within the coating. Thus, where a chemically amplified resist is used as a photoresist, acid molecules generated in the resist layer upon exposure are partly trapped by the amino groups of the substrate, resulting in footing of resist profile with positive-working resists or resulting in undercutting (bite) with negative-working resists. On the other hand, with an anti-reflective coating composed of an organic coating, too, an acidic or alkaline component sometimes can remain on the surface of the coating and similarly causes footing or undercutting of resist profile. Such phenomena are not limited to the case where the bottom anti-reflective coating is provided, but can similarly take place in the case where other coating (e.g., ITO coating) than the bottom anti-reflective coating is formed on the substrate or where a photoresist is directly applied to the substrate. In addition, this is not limited to the case where a chemically amplified resist is used as a photoresist, but those photoresists wherein an acidic or alkaline component exists or wherein an acidic or alkaline substance is formed in the course of resist pattern-forming steps which are in turn utilized for forming a resist pattern, the resulting resist profile will be adversely affected by the substrate as with the chemically amplified resists, thus patterns with good form not being formed.
Heretofore, analysis of the surface state of these substrate materials and processing of substrate surface by plasma treatment or the like for improving adhesion of the substrate surface have been attempted. Techniques relating to improvement of such art are described in J. S. Sturtevant et al, Proc. SPIE, 2197, 770 (1994); K. Dean et al, Proc. SPIE, 2438, 514 (1995); S. Mori et al, J. Photopolymer Science and Technology, 9, 601(1996); B. C. Kim et al, Proc. SPIE, 2724, 119(1996), and the like. However, they do not describe pre-treatment technology of applying a surface-treating agent to a substrate.
An object of the present invention is to provide a method for preventing detrimental influences due to uneven acidity of or within a substrate on the form of resist pattern in case where an acidic or alkaline component exists in a photoresist like a chemically amplified resist or where a photoresist is used in which an acidic or alkaline substance is formed in the course of resist pattern-forming steps, said substance being utilized for forming a resist pattern, and a composition of a substrate-treating agent to be used in the method.
As a result of intensive investigations, the inventors have found that a resist pattern with no defects described above can be formed by treating a substrate with a specific treating agent before applying thereto a photoresist, thus having achieved the present invention based on the finding.
That is, the present invention is a technique of treating a substrate on which a resist pattern is to be formed, and relates to a substrate-treating agent composition composed of a solution containing a salt between at least one basic compound selected from the group consisting of primary, secondary and tertiary amines and nitrogen-containing heterocyclic compounds and an organic acid of a sulfonic acid, carboxylic acid or the like, and to a method of forming a resist pattern which comprises treating a substrate with the aforesaid substrate-treating agent composition and, after baking, applying thereto a photoresist, then conducting exposure and development.